1. Field
Aspects of this disclosure pertain to a method and system of coating a polymer solution such as a photoresist polymer solution over a surface of a substrate such as silicon substrate.
2. Discussion of Related Art
The manufacture of integrated circuits involves the transfer of geometric shapes on a mask to the surface of a semiconductor wafer. Thereafter the semiconductor wafer corresponding to the geometric shapes or corresponding to the areas between the geometric shapes is etched away. The transfer of the shapes from the mask to the semiconductor wafer typically involves a lithographic process. This includes applying a photosensitive pre-polymer solution to the semiconductor wafer. The solvent in the pre-polymer solution is removed by evaporation, and the resulting polymer film is then baked. The film is exposed to radiation, for example ultraviolet light, through a photomask supporting the desired geometric patterns. The images in the photosensitive material are then developed by soaking the wafer in a developing solution. The exposed or unexposed areas are removed in the developing process, depending on the nature of the photosensitive material. Thereafter the wafer is placed in an etching solution which etches away the areas not protected by the photosensitive material. Due to their resistance to the etching process, the photosensitive materials are also known as photoresists. These may for instance be sensitive to ultraviolet light, electron beams, x-rays, or ion beams.
Systems and methods have been developed for the dispensing the photoresist solutions on a substrate. Typically, the system includes a pump connected to a reservoir containing a photoresist solution. The reservoir may be filled with the photoresist solution from a photoresist solution source. A vacuum source can typically be used to transfer the photoresist solution from the source into the reservoir. One problem with the current systems and methods is the non-uniformity in the photoresist film of photoresist coated on the substrate. For instance, when the photoresist solution source is low and required changing, micro bubbles and air may get into the system causing non-uniformity in the photoresist film. Additionally, when the vacuum is used to transfer the photoresist solution, splattering tends to occur in the reservoir causing the viscosity of the polymer solution to change or increase over time and inhibiting the leveling of the resulting film. This produces thickness non-uniformities in the photoresist film.
The high cost of the photoresist solutions (or other polymer solutions) makes it desirable to devise methods of improving the efficiency of the coating process so as to minimize the polymer solution's consumption. Furthermore, thickness uniformity of the photoresist layer is an important criterion in the manufacture of integrated circuits. It ensures satisfactory reproduction of the geometric patterns on the semiconductor wafer.
The features of the described embodiments are specifically set forth in the appended claims. The embodiments are best understood by referring to the following description and accompanying drawings, in which similar parts are identified by like reference numerals.